Vehicle intrusion alarm system

ABSTRACT

A vehicle intrusion alarm system protects against the pilferage of vehicles, such as trucks, that remain overnight or longer on parking lot. The system is based on the cooperation between a receiver in the parking lot and a transmitter in the vehicle, said transmitter adapted to be activated by the mere act of opening a vehicle door. As soon as an intruder opens such a door, this action causes the transmitter to produce a changing magnetic field; and a pickup wire of the receiver produces a signal voltage that is used to produce an alarm.

United States Patent DAusilio et al. 1 Aug. 29, 1972 [54] VEHICLEINTRUSION ALARM [56] References Cited SYSTEM UNITED STATES PATENTS [72]22:: gag 3,164,802 1/1965 Kleist et a1. ..340/ 2ss c x Beach both ofCalif. 1 3,541,347 11/1970 Carmack 340/258 C [73] Assignee: ThresholdEngineering, Inc., Fuller- I Primary Examiner-Alvin Waring ton, mAttorney-Francis X. LoJacono [22] Filed: April 28, 1971 5 ABSTRACT PP ,2A vehicle intrusion alarm system protects against the pilferage ofvehicles, such as trucks, that remain overnight or longer on parkinglot. The system is based on 52 US. Cl. ..340/63, 340/51, 340/276, thecooperation between a receiver in the parking lot 325/64 325/117 and atransmitter in the vehicle, said transmitter d pted to b activated themere act of opening a Fleld 0f Search vehicle door. As soon as anintruder opens such a door, thisaction causes the transmitter to producea changing magnetic field; and a pickup wire of the receiver produces asignal voltage that is used to produce an alarm.

19 Claims, 9 Drawing Can /r 0/ Um Patented Aug. 29, 1972 5 Sheets-Sheet2 can /ro/ UNI I Con/rel [/n if Patented Aug. 29, 1972 5 Sheets-Sheet 4.

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VEHICLE INTRUSION ALARM SYSTEM BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates, generally, to an intrusion alarmsystem and, more particularly, to a vehicle intrusion alarm system whenthe vehicle is parked in a particular given area.

2. Description of the Prior Art As is well known, many vehicles carry avaluable cargo, ranging from tools to products (e.g., plumbers tools,television repairmans equipment, dictating machines, salesmans samples,telephone equipment, etc.); and in many cases it is impracticable tounload the vehicle every night.

It is becoming increasingly more difficult to prevent pilferage fromthese parked vehicles and many schemes have been suggested for solvingthis problem. Unfortunately, most of these prior-art schemes arecomplex, expensive and subject to human error, such as forgetting toturn them on and consuming too much power from the vehicle system.

The present intrusion alarm system solves the above problems in asimple, fool-proof manner.

The following brief discussion of prior-art intrusion systems willprovide an understanding of the problems, and of the operation andadvantages of the disclosed system. For ease of comprehension, it willbe presented in terms of a truck parked on a parking lot, but it will beapparent that the disclosed invention has many other uses.

Many of the prior-art intrusion systems provided an alarm when anintruder touched, approached or passed a given barrier, such as a fence,but gave no alarm if the intruder somehow by-passed the barrier (as, forexample, by being within the barrier when the intrusion system wasturned on). In cases such as these, parked vehicles and the like couldbe pilfered at leisure without producing an alarm, the alarm beingproduced only when the intruder was already escaping with his loot. Someother intrusion systems produced an alarm when a body moved within apredetermined area, but due to the required sensitivity of such a systemthe protected area had to be quite small. Other intrusion systemsproduced an alarm when a vehicle was driven across a given sensor suchas a wire, a lightbeam, an air hose or the like, but such systems didnot give any warning that pilferage was impending. Still other systemshad alarms attached to the vehicle proper, the concept being thatwhenever the vehicle was jarred the alarm would sound.

However, most of the prior-art intrusion systems were subject toproducing false alarms, and most of them had to be deenergized duringdaytime activities. Otherwise, they would sound nuisance alarms atundesired times. Moreover, someone had to remember to re-energize theintrusion system when the vehicle was parked for the night.

As may be realized from the above discussion, despite the wide varietyof available intrusion systems, none of these prior-art systems werecompletely satisfactory.

SUMMARY OF THE INVENTION Broadly stated, the disclosed intrusion alarmsystem is based on the principle that a changing magnetic field causes apickup wire to. produce a signal voltage. The present applicationdiscloses a variety of transmitters for producing such a changingmagnetic field; one of the transmitters comprising a magnet afiixed to atruck door, another transmitter comprising an electromechanical means,and another transmitter comprising electronic circuitry. In any case,the changing magnetic field produced by the transmitter induces a signalvoltage in a pickup-wire portion of a receiver, and the disclosedcircuitry causes the signal voltage to produce an alarm.

Additional circuitry is disclosed for minimizing false alarms and forpreventing undesired discharge of the vehicle-power system.

OBJECTS AND ADVANTAGES OF THE INVENTION It is, therefore, the principleobject of the present invention to provide an improved intrusion alarmsystem.

It is another object of the present invention to provide an improvedintrusion alarm system for producing an alarm when a properly equippedvehicle is parked at a properly equipped parking lot.

It is still another object of the present invention to provide animproved intrusion alarm system that is automatic, and is immune tohuman error.

It is a further object of the present invention to provide an improvedintrusion alarm system that is practically impossible to disable priorto intrusion.

It is a still further object of the present invention to provide animproved intrusion alarm system that is simple, inexpensive and easy tomanufacture.

A still further object of the present invention is to provide an alarmwhenever the vehicle is raised along any portion thereof to prevent tiretheft.

DESCRIPTION OF THE DRAWINGS The attainment of these objects, and others,will be realized from a study of the following description, taken inconjunction with the drawings, of which:

FIG. 1 shows a portion of a parking lot and a truck parked thereon andtheir cooperation in producing an intrusion alarm;

FIG. 2 shows a portion of a parking lot with an alternative sensingunit;

FIG. 3 shows another parking lot having trucks parked thereon, and theircooperation in producing an intrusion alarm;

FIG 4 shows a portion of the utilization circuitry;

FIG. 5 shows a truck incorporating the transmitter portion of theintrusion alarm system;

FIG. 6 shows a schematic diagram of an electronic means andelectro-mechanical means of the transmitter portion of the system;

FIG. 7 shows a schematic diagram of the receiver portion of the system;

FIG. 8 shows a schematic diagram of the electromechanical system; and

FIG. 9 is an elevational view of a cam plate used in theelectro-mechanical system.

Principles of Operation It is well known that an electrical conductor,such as a wire, produces an electrical voltage when it is exposed to achanging magnetic field, the resulting electrical voltage depending inpart on the magnitude of the magnetic field, on the rate at which themagnetic field is changing and on other factors.

- The disclosed intrusion alarm system is based on the above principle.A receiver, comprising a length of wire, is positioned at a parking lotwherein a vehicle is to be parked, so that when this receiver wire isexposed to a changing magnetic field it will produce an electricalvoltage as described above. The manner of producing this electricalvoltage will be discussed more fully later.

The receiver further comprises a control unit for amplifying theelectrical voltage, controlling various factors such as possible falsealarms, etc., and for actuating a utilization device.

The utilization device, a number of forms of which will be discussedlater, uses the output of the control unit to provide an alarm of thedesired type.

The transmitter-three types of which will be discussed-provides achanging magnetic field in the vicinity of the receiver wire when a doorof the parked truck is opened, regardless of whether the door was openedby a key or was forced open.

Referring now to FIG. 1, there is illustrated a portion of a parking lothaving a plurality of dividers 11, which may be painted stripes,concrete bumpers, or the like, to provide a plurality of defined parkingspaces. A truck 12 is indicated to be positioned in one of the definedparking spaces, several of the truck doors 13a, 13b, 130 being shownopened to different degrees. Parking lot 10 may have a length and widthof, typically, 1,000 feet and 200 feet, respectively; and may, ifdesired, have surrounding fence.

It will be noted that in FIG. 1 parking lot 10 is shown to have aperipherally-positioned pickup loop 14, illustrated as comprising asingle turn of wire; but, as is known to those skilled in theelectronics art, more turns of wire may often be advantageously used. Itwill also be noted from FIG. 1 that the configuration of pickup loop 14is such that it has a plurality of secondary loops 15, so that a lengthof pickup-loop wire 16 extends along each of the defined parking spacesand across the back of each parking space. The reason for thisparticular pickup-loop configuration will become apparent from thefollowing explanation.

Pickup loop 14 may be formed of any suitable electrically conductivewire of lumped coil of wire, since the electrical voltage producedtherein is quite small (in the order of about five microvolts); and,furthermore, there is very little actual flow of electric current inloops 14/15. It should be realized, however, that the wire of the pickuploop may be exposed to weathering, may be subjected to the action oftires rolling across it, may have to withstand scuffing from the shoesof pedestrians, etc. Therefore, the loop wire is preferably mechanicallystrong.

The loop wire may be fastened to the surface of the parking lot by meansof adhesives, by the use of adhesive tapes, etc.; but the loop wire ispreferably buried beneath the surface of the parking lot either byslotting the parking surface and burying the wire or by incorporatingthe wire into a new parking surface, or the like. It has been foundthat, when buried in the above described manner, ordinary insulated wireis completely satisfactory, and has a suitable life and freedom fromgalvanic action. However, the loop wire may be installed in metal orplastic conduits around the margin of the enclosed area.

As indicated in FIG. 1, the ends of pickup loop 14 are connected to acontrol unit 17 that will be discussed later in greater detail; andcontrol unit 17 is, in turn, connected to a utilization device 18a,indicated in FIG. 1 to be a horn.

Transmitter I FIG. 1 indicates a truck 12 positioned in one of thedefined parking spaces, the truck having a plurality of standard andsliding doors 13. When necessary, magnets (not shown) are affixed in anysuitable manner to the doors, it being preferable that the magnets areat the outer lower corners of the doors, so that they are as close aspossible to the ground, and thus as close as possible to the wires 16 ofthe secondary pickup loop 15.

It will be realized that, when any of the doors 13 are opened, the doorwill sweep loop wire 16, as indicated by arrows 19. This movement of thedoor and its associated local earths magnetic field is such that aportion of the loop wire 16 is exposed to a changing magnetic field.

To be more specific, when a truck door is first opened (see door 13a),the loop wire is exposed to a weak changing magnetic field produced bythe relatively distant ferro-magnetic doors; when the door has opened tosuch a position that the door is directly above the wire (see door 13b),the wire is exposed to a stronger magnetic field; and when the door isopened even wider (see door 13c), the door is then located on the otherside of the wire, so that the wire is now exposed to a weaker magneticfield previously. previously. Thus, regardless of the exact spatialrelation between the magnet and the wire, and regardless of the amountthat the door is opened, the loop wire 16 is exposed to a changingmagnetic field.

Therefore, as explained above, an electrical voltage is induced in thepickup-loop wire; and this voltage is applied, as a signal, to thecontrol unit 17. It will, of course, be realized that the signal voltagemay be stronger at some times than at othertimes,'depending upon theheight of the door above the wire, depending upon the parking positionof the truck, depending upon the rate at which the door is opened, etc.;but the opening of the truck door by an intruder will produce asignal'voltage, and electronic circuitry, to be discussed later,compensates for these various factors. However, an alternativearrangement of a lumpwire unit 15a, as shown in FIG. 2, can be used inplace of pickup loop 15.

Thus, it will be recognized that, whenever such a suitably equippedtruck is parked at a suitablyequipped parking lot, the cooperativesystem of the transmitter and the receiver will automatically produce analarm in the event of truck intrusion.

It should be noted, however, that when the truck is being used duringits assigned duties the opening and closing of its doors at locationsother than the protected parking lot do not produce nuisance alarms.However, when the truck has completed its assigned duties, and is parkedin any one of the defined parking spaces, the disclosed intrusion alarmsystem automatically goes into operation.

Another unexpected advantage accrues to the disclosed intrusion alarmsystem; namely, it provides an alarm if the trucks engine is startedpreparatory to stealing the truck. s such a case, the mere turning onthe trucks ignition system produces a surge of electricity from thetrucks battery; the rotation of the trucks starting motor causes anextremely large flow of electric current; and the resulting activationof the trucks generator or alternator produces a current flow. Each ofthese electric-current flows produces its own changing magnetic filed;and, therefore, produces a signal voltage and'a resulting alarm.

There is shown in FIG. 3 the configuration, which again illustrates aparking lot 20, having a plurality of trucks 12 parked thereon; but, inthis case, defined parking spaces are no longer needed. Parking lot 20has a pickup loop 21, comprising a suitable number of turns, four suchturns being indicated. Pickup loop 21 preferably encircles the parkinglot, but the previously disclosed secondary loops are unnecessary. Thus,pickup loop 21 has a much simpler configuration and is much cheaper toinstall.

The ends of pickup loop 21 are connected, as previously discussed, to acontrol unit 17; and the output of control unit 17 is applied to autilization device 18b, in dicated to be a rotating lightbeam air-patrollight that may be mounted on a pole, on a tower, on a rooftop, etc. Whenthis light is actuated, its rotating lightbeam instantly attracts theattention of patrolling aircraft.

Still another type of utilization device We is indicated in FIG. 4. Thisis a self-dialer that is connected to the telephone lines. When theself-dialer 180 is actuated by a signal from control unit 17, it mayoperate in either of two modes, depending upon its type. The first modeof operation is such that is self-dials a predetermined telephonenumber, and then telephones a given tone (either a steady unmodulatedtone or a modulated tone that quavers), so that a person, or equipmentat the predetermined number can determine the location of the intrusion.Alternatively, in the second mode of operation, the self-dialer alsodials a predetermined number, but then it plays a taped recording thatidentifies the location of the intrusion.

Referring back to FIG. 3, the pickup loop 21 indicated thereon operatesin basically the same manner as previously discussed; that is, when aportion of it is exposed to a changing magnetic field, it produces asignal voltage that is applied to control unit 17. The generation ofthis changing magnetic field will now be discussed.

The improved transmitter does not use the previously discussed truckdoors; rather, this transmitter, as may be seen from FIG. 5, comprises asending loop 26, of one or more turns of wire, that is mounted on truck12. For the reasons to be discussed later, the sending loop 26 shouldpreferably be mounted horizontally and as close to the ground aspossible. However, because of vehicle construction and the desire tolocate the sending loop 26 in a tamper-proof location, the preferredmounting is not always available; and in one particular case it wasfound that the optimal location for the sending loop 26 was within thevehicle in its roof channel.

By means to be discussed later, an intrusion causes the sending loop 26to conduct a periodically changing electric current; and this changingelectric current produces a changing magnetic field. Since a portion ofthe pickup loop is spatially located in this changing magnetic field,the pickup loop produces a signal voltage that is used to produce analarm.

It is obvious that the sending loop 26 of FIG. 5 should produce itschanging magnetic field only at the time of an intrusion; and thisresult is achieved by affixing an electrical switch at each door of thetruck (and at its hood, windows, skylight, etc., when desired),regardless of the manner in which they open. These electrical switchesare then used to initiate the changing magnetic field.

In the simplist form of the improved transmitter, each door to beprotected has its own electrical switch, say one of the mechanicalelectrical switches that are used to turn on the dome light when thedoor is opened. However, rather than turning on the dome light,.thismechanical electrical switch is used to actuate a thermal switch in theform of a flasher of the type used for the turn signal indicating lamps.It is also obvious that other thermal switches may be used in thissystem. The now actuated flasher directs intermittent pulses ofelectricity from the vehicles battery through sending loop 26, theseintermittent pulses of electricity causing sending loop 26 to produce achanging magnetic field, which in turn causes the pickup loop 21 (ofFIG. 3) to produce a series of signal voltages.

However, an alternative arrangement can replace the flasher unit whichincorporates its function into a miniaturized electronic printing wiringboard that also contained pulsing circuitry, along with replacing themechanical electrical switch with a normally open magnetic-reed switch(such as magnet model No. 1834-607 and switch model No. MRR-2-185 madeby I-Iarnlin, Inc.) that was rated at one-million cycles of operation atthe desired load.

FIG. 5 indicates that truck 12 hasa plurality of such switches 28mounted at each door and engine hood to be protected, and centrallypositioned mercury switches 28 mounted at the front and rear areas ofthe vehicle, respectively. These normally open switches 28 are heldelectrically closed by associated magnets 29 affixed to the doors of thetruck. Thus, during the quiescent period, magnets 29 hold switches 28 ina closed state, and no electric current is permitted to flow from thetruck battery; but, whenever a door is opened, the magnet 29 is movedaway from its associated switch 28, the switch reverting to its normallyopen state, and thus permitting electric current to flow from thevehicle battery to the pulsing circuit, to be described later.

In this way, when the truck is parked at a protected parking lot, anintrusion that opened any door of the truck automatically opened themagnetic switch at that door, thus activating the pulse circuit andcausing the sending loop 26 to produce a changing magnetic field, thischanging magnetic field being picked up by the generally occur when, forexample, tires of the vehicle were about to be removed.

It should be noted that while the truck is being used in its dailyassigned duties, away from the protected parking lot, the act of openingthe doors still produces a changing magnetic field; but since there isno suitable pickup loop in that vicinity, no alarm is produced.

As indicated in FIG. 5, the various switches 28 and 28a may be connectedin series and connected over a common bus wire to pulsing-circuitcontainer 30. This particular wiring arrangement requires that thepulsingcircuit container 30 accept only a single wire from the switches28, two wires from the sensing loop 26 and two wires from the truckbattery; and this, of course, simplifies the problem of externalconnections to the pulsing circuit. Moreover, the container 30 of thepulsing circuit is not grounded, so that it may be mounted at anyconvenient location in the truck. A screwed-down connection forgrounding purposes is not necessary. Thus, a pulsing-circuit container30 which is somewhat smaller than a package of cigarettes may be merelytaped down, or even left unattached. Because of this wiring arrangement,it is convenient to remove the entire sending loop 26, thepulsing-circuit container 30, the switches 28 and, if desirable, themagnets 29 any time that the system is to be re-installed in anothertruck.

It was previously pointed out that the sending loop 26 is preferablyhorizontal and as close as possible to the ground, and, therefore, asclose as possible to the pickup loop 21; and the reason for this will beunderstood from the following discussion. The interaction of twomagnetic loops or two magnetic fields is known as their mutual coupling,a tight coupling being associated with a close mutual coupling. Sincethe disclosed pickup loop is horizontal, and is at or buried slightlybelow the parking lot surface, optimal mutual coupling is obtained whenthe sending loop is also horizontal and as close as possible to thepickup loop. This desideratum isnt always achievable but it should beapproached as closely as possible.

Ordinarily, a ferrous material, such as iron that is placed between twomagnetic loops tends to act as a magnetic shield and tends to minimizemutual coupling. Surprisingly, however, the metal truck body (which ismade of iron and seems to be placed between the sending loop and thepickup loop) does not introduce a shielding effect; if anything, itseems to enhance the coupling between these two loops. Relatively littleseems to be known about the coupling of large loops as used in thisinvention and it appears that the metal body of the truck acts as a corethat improves the magnetic coupling.

It will be apparent that the strongest signal voltage is obtained fromthe pickup loop when the truck has been parked as close as possible tothe peripheral pickup loop 21; but it has been found that by properselection of the number of turns in the loops, by proper design of thecircuit parameters, by suitable choice of amplifier gain, by use ofsufficient battery current, etc., a suitable-strength signal voltage maybe obtained from the pickup loop, even when the truck is parked anappreciable distance from the edge of the parking lot. This increasedsensitivity provides an additional advantage; namely, a late arrivingtruck may be parked outside of the locked fence and still be protectedby the disclosed intrusion alarm system. Polarity loops may be coupledin phase or out of phase to prevent the system sensitivity fromdecreasing whenever the loops are out of phase. The transmitter is madeto generate a bipolar pulse.

It was pointed out above that when any of the truck doors are opened achanging magnetic field is produced, and FIG. 6 shows an electroniccircuit that may be used for this transmitter function. The circuit ofFIG. 6 comprises five co-acting circuits that will be discussed later ingreater detail. The five circuits are as follows: a timing circuit 31,an oscillator circuit 32, a flip-flop circuit 33, an amplifier-circuitdriver 34, and a damping circuit 35. Basically, these circuits co-act inthe following manner.

When any of the doors of the truck are opened, the timing circuit 31 isactivated; and this circuit thereupon provides operating power for allthe subsequent circuitry, except transistor 57, for a given interval oftime. The operating power provided by the timing circuit 31 actuates theoscillator circuit 32, which thereupon provides trigger signals to theflip-flop circuit 33, this latter circuit producing aperiodically-reversing electric current. The reversing current is thenapplied to the sending loop 26 located in the truck, this loop thenproducing the desired reversing (changing) magnetic field. The dampingdiode 35 minimizes the danger from high-back electromotive force.

Timing Circuit Referring again to FIG. 6, the upper left hand portion ofthis drawing shows a plurality of switches 28 that represent the doorswitches on the truck. A plurality of magnets 29 are indicated asholding switches 28 in a conductive state during the quiescent no-alarminterval.

During this quiescent state, the timing circuit 31 is in its standbystate, as follows. With all the switches 28 closed, as indicated, thereis no signal being applied to the input terminal 36 of the timingcircuit 31; or, stated in another way, input terminal 36 is grounded atbattery potential due to the action of resistors 39 and 44. 43 is atground potential due to the action of transistor 49.

Diode 48 transmits the battery potential at point 42 to the baseelectrode of transistor 49, so that transistor 49 is saturated on andtransistor 50 is cut off since its base electrode potential is too lowto permit conduction. Therefore, during the quiescent period, there isno output signal at the timing circuit output terminal 51; in fact,output terminal 51 is at substantially ground potential due to thenon-conductivity of transistor 50 and this ground potential istransmitted over wire 52 to hold transistor 53 in its non-conductingstate during the quienscent period.

In summary, it will be seen that when all the truck doors are closed thequiescent state of timing circuit 31 does not produce an output signal.

When any of the truck doors is opened, the quiescent state of the timingcircuit 31 is changed to an active state, as follows. The opening of adoor causes its associated door switch 28 to assume its electricallyactivated condition; and this condition removes the grounding potentialto the input terminal 36 of the timing circuit. Now, due to the actionof resistors 37 and 38, diode 54, resistor 39, capacitor 55 and 55',resistor 44 and diode 48, the base electrode of transistor 49 isdownvolted,i.e., has its erstwhile high potential lowered; andtransistor 49 becomes non-conductive.

This condition, in turn, upvolts point 43 and causes transistor 50 tobecome conductive; and now there is an output on terminal 51. Thisoutput signal is applied, over wire 56, as an operating power toactivate the subsequent portions of the pulsing circuit, the operationsof these subsequent portions to be discussed later.

With the production of an output signal at output terminal 51 of thetiming circuit 31, this output signal is also applied over wire 52 tothe base electrode of transistor 53, turning this transistor on to itsconductive state. The non-conductive transistor 53 has the followingeffect; namely, it electrically connects (clamps) point 41 to groundpotential. Now, even if the previously opened truck door is quicklyclosed, thus electrically closing its associated door switch, point 41remains electrically clamped to ground; and timing circuit 31 maintainsits active state, thus negating the effect of closing the truck dooronce the intruder enters the truck.

The active state of the pulsing circuit would be maintained until it isturned off manually but this active state may completely discharge thetruck battery. In order to avoid this possibility, the duration of theactive state is terminated in the following manner. When point 41 isclamped to ground potential by conductive transistor 53 in the mannerpreviously described, capacitor 55 assumes an entirely differentenvironment. Previously, during the quiescent state, both sides ofcapacitor 55 were at substantially battery potential, so that capacitor55 assumed a quiescent state. During the active state, however, the leftside of capacitor 55 has been downvolted to ground potential by the nowconductiveclamping transistor 53; the right side of capacitor 55 stillbeing connected through resistor 44 to battery potential. As a result,electricity starts to flow through capacitor 55 but, since it is acapacitor, it has the inherent characteristic that it charges up; thatis, its left side remains clamped to ground potential but its right sideis gradually upvolted to assume progressively higher potentials. As aresult, point 42, which is electrically connected to the upvolting sideof capacitor 55, is also gradually upvolted and, acting through diode48, gradually upvolts the base electrode of transistor 49. Eventually,the base electrode is upvolted to such a value that transistor 49 isturned on to its conductive state, thus turning off transistor 50 andterminating the output signal at output terminal 51.

The termination of the output signal has two simultaneous effects. Thefirst of these is that it turns off clamping transistor 53 and thisaction unclamps point 41 from ground potential, reestablishing thefunctioning of door switches 28. The second effect is that it terminatesthe operating power applied over wire 56 to the subsequent portions ofthe pulsing circuit.

To summarize the operation of the timing circuit, it responds to theopening of a door by activating the entire pulsing circuit for a giveninterval of time, after which it returns the entire pulsing circuit to aquiescent state.

The establishment of selected timing intervals is well known to thoseskilled in the electronics art. These time intervals are readilyobtained by the use of socalled resistor/capacitor combinations and thistechnique has been used in the disclosed circuitry. Referring back toFIG. 6, it will be seen that, during the active interval, while the leftside of capacitor 55 is clamped to ground potential its upvoltingcurrent flows to capacitor 55 through resistor 44. Therefore, the valueof resistor 44 has a major effect on the amount of electricity thatflows into, and charges, capacitor 55. Moreover, the value of capacitor55 itself also has a major effect on the rate at which it is charged up.Therefore, the values selected for the resistor 44/capacitor 55combination establish the time interval during which the timing circuitwill remain active. In the present case, the active interval is about 10seconds, for reasons to be discussed presently.

Another thing should be noted about timing circuit 31; namely, once itsactive time interval has been reached, the timing circuit should bereturned as quickly as possible to its quiescent state, in order thatcontrol is restored to the door switches, so that the system is free toreport other intrusions. This quick return is accomplished as follows.Once clamping transistor 53 becomes non-conductive, resistor 39 quicklyupvolts the now unclamped left side of capacitor 55 connected to point41. Resistor 39 is selected to have a relatively small value, so thatthe upvolting effeet is practically instantaneous.

Thus, once a truck door is opened, timing circuit 31 becomes activatedfor a given time interval, meanwhile activating a subsequent pulsingcircuit for the same active time interval. At the end of the activeinterval, the entire pulsing circuit quickly returns to its quiescentstate, ready to report another intrusion.

Oscillator Attention is now directed to oscillator circuit 32 of FIG. 6.While any of a plurality of oscillator circuits may be used, FIG. 6illustrates a type known as a unijunction oscillator, due to the use ofuni-junction transistor 57 therein. This particular type of oscillatoris convenient because it produces, not only a sawtooth waveform (whichis not used in the present circuit), but also produces a spike" waveform58 at output terminal 59, the spikes recurring in this case at a typicalrate of about 10 per second. During the active interval, the spikewaveform 58 is applied, over wire 61, to flipflop 33.

Flip-Flop It is known to those skilled in the electronics art that thereis available a large variety of circuits known as flip-flops", thesehaving the characteristic of flipping" between pre-established states.The flip-flop circuit 44 of FIG. 6 has two stable states (comparable tothe two stable states of the usual light switch). During the activeinterval, the train of spikes in spike waveform 58 is appliedcontinuously from oscillator 32, over wire 61,

to flip-flop 33. Here a given spike acts as a trigger signal that causesthe flip-flop circuit 33 to flip" to one of its, stable states. The nextspike acts as a trigger signal that causes the flip-flop circuit to flopback to its original stable state. The subsequent spike acts as atrigger signal that causes the flip-flop circuit to again flip to itsother stable state. This flip-flop action continues as long as suitablespike signals are applied to the flip-flop circuit.

It is a characteristic of flip-flop circuit 33 that its output terminal62 produces a square wave waveform 63; and this waveform 63 has arepetition rate, or frequency, that is half that of the applied spikewaveform 58, i.e., about cycles per second.

Driver/ Amplifier For amplification, the square-wave waveform 63 at theoutput terminal 62 of flip-flop 33 is applied to a driver/amplifier 34,which may be a signal transistor, a series of cascaded transistors, aversion of the wellknown Darlington circuit, etc. In any case, theoutput of driver/amplifier 34 is applied to sending loop 26 which ismounted on the truck and here it causes pulses of reversing electriccurrent to flow through the sending loop. These reversing-current pulsesof electricity cause the sending loop 26 to produce reversing (changing)magnetic fields.

Damping Diode It is known that when a reversing magnetic field isproduced it may induce dangerously large voltages. In order to dissipatesuch large voltages, a damping diode 35 is connected across theterminals of the sending loop 26.

To recapitulate, once a truck door is opened, its as sociated doorswitch activates the timing circuitry for a predetermined interval oftime. The output of the timing circuit, in turn, activates thesubsequent pulsing circuitry, to cause the sending loop to produce aperiodically reversing magnetic field for the duration of the activetime interval.

Typical Numerical Values It will be recalled from the previousdiscussion that timing circuit 31 is activated for a time interval ofabout seconds; that oscillator circuit 32 has a frequency of about 10I-Ierz (cycles per second); and that flip-flop circuit operates at abouthalf that frequency, resulting in about five reversing pulses persecond. Therefore, once a truck door is opened, its associated doorswitch initiates an active interval that produces about fifty (10 X 10/250) magnetic fieldreversals, whereupon the entire pulsing circuitreverts back to its quiescent state. The reason for these numericalvalues will become apparent from a latter discussion of the receivercircuitry.

Receiver It will be recalled that the receiver comprises a pickup loop(21 of FIG. 2) that is preferably buried beneath the surface of theparking lot; and that every time that the sending loop 26 in the truckproduces a change of magnetic field, pickup loop 26 produces a signalvoltage, Since the pulsing circuit of FIG. 6

produces about 50 changes of the magnetic field, the pickup loop 21produces about 50 signal voltages.

FIG. 7 illustrates a schematic diagram of an electronic circuit for sucha receiver. As shown, pickup loop 21 applies the signal voltages to awell known operational amplifier 66; this amplifier using well knownfrequency compensation components 67, 68 and 69. Operational amplifier66 also has gain-control components 71 and 72, and low-frequency bypasscomponent 73.

Briefly stated, these components are desirable for the followingreasons. As pointed out above, the signal voltages in the pickup loop 21appear at a rate of about 5 per second; and the frequency-compensatingcomponents form a network that enhances the ability of the amplifier toamplify signals of this frequency.

Gain resistors 71 and 72, along with design parameters, causeoperational amplifier 66 to achieve a gain of about 600. As a result, agreatly amplified signal voltage appears at the output terminal 77 ofthe operational amplifier 66.

At output terminal 77, a de-coupling capacitor 78 permits the amplifiedsignal voltage to be applied to a subsequent amplifier 79, which may bea second operational amplifier designed capacitor 78 and resistor 81form a high-frequency pass network.

As indicated, the output of the second operational amplifier 79 isapplied to the base electrode of a transistor 82, whose output is thenapplied to subsequent transistors 83, 84 and 85. While varioustransistor configurations and interconnections may be used, FIG. 7 showsthe two latter transistors to be connected in a Darlington arrangementto provide highinput impedance at base electrode of 84 while providinglow-output impedance at emitter electrode of transistor 85.

The final output of transistor 85 is applied to a relay 88 to turn on analarm-type utilization device 18.

Theoverall operation of the receiver, since there is no danger ofdischarging a battery, is such that it is always in its active state.-When a signal voltage is received from pickup loop 21, it is immediatelyamplified and turns on the alarm-type utilization device 18.

False Alarms A slight digression is desirable at this time, to discussthe problem of false alarms. In order to detect all intrusions, evenunder those conditions when the signal voltage from the pickup loop isquite weak, the circuitry of all intrusion systems is designed to have ahigh overall amplification. Unfortunately, a high amplification meansthat many spurious signals will be amplified to a large enough value sothat the circuitry will treat them as though they were legitimateintrusion signals, thus producing a false alarm.

In the present case, the spurious signals may take the form of achanging magnetic field caused by changes in the variations of theearths magnetic field, by electrical surges in nearby power lines, bypassing traffic that may have magnetic characteristics, and the like. Inorder to avoid false alarms produced by such spurious conditions,reference is made to the foregoing discussion that a true intrusion intoa protected truck will result in a train of about 50 signal voltagesproduced in a time interval of about 10 seconds. It is extremelyimprobable that spurious magnetic field variations would produce anysuch train of timed signal voltages, and the disclosed receiver circuittakes advantage of this situation in the following manner.

Referring to the receiver circuit of FIG. 7, the signal induced in loop21 is accepted by amplifier 66 whose gain is controlled by resistors 71and 72. This configuration is the well-known, voltage-follower,operationalamplifier circuit and has a voltage gain of about 600.Amplifier 79 is a similar circuit having a voltage gain of about 100 andis coupled to amplifier 66 and output 77 by means of capacitor 78.Output 77 is coupled through capacitor 78 and in the presence of asignal causes transistor 82 to turn on and off which in turn pulsestransistor 83, thereby charging capacitor 93.

Capacitors 73 perform the function of a low-pass filter to reject 601-12power line interference. Capacitor 78 in conjunction with resistor 81form high-pass filters, and in combination with the low-pass elementsfrom an efiective band pass characteristics whose maximum response isthe same as the pulser repetitive rate.

Thus, during the first signal voltages, the counting means disables thereceiver circuit so that it does not produce an output signal; but thefifth signal voltage charges up capacitor 93 to the potential thatpermits transistor 84 to become conductive. Therefore, the sixth signalvoltage (and the subsequent 44 signal voltages) pass through the entirereceiver circuit and produce an alarm as discussed above.

The utilization device 18, therefore, produces a series of about 45 hornblasts, light flashes, or the like. Alternatively, relay 88 may be ofthe latching type to produce a continuous hornblast, a continuouslyrotating lightbeam, or the like, relay 88 unlatching itself after apredetermined time interval or manually by the user.

Thus, the disclosed counting circuit counts the first five signalvoltages to appear and holds the output circuit disabled during thistime interval in order to prevent false alarms, but permits a trueintrusion to sound the alarm.

It should be noted that sending loop 26 is operated for a very shortinterval, of about ten seconds, from a substantially fully-charged truckbattery, so that an appreciable amount of battery power is available,thus producing a strong changing magnetic field. As a result of thestrong changing magnetic field, the pickup loop 21 produces a strongsignal voltage, and this strong signal voltage further minimizes theprobability of false alarms.

Circuit Protection Referring back to the receiver circuit of FIG. 7, thefirst operational amplifier 66 is designed to include acircuit-protection means so that there is normally a slight voltage atits upper input terminal during the quiescent portion of the systemsoperation, so that this slight voltage will cause a minute electriccurrent to flow through the pickup loop 21 during the quiescent portionof the systems operation. This small electric current is used in thesystem design as part of the quiescent no-alarm condition, since thesystem responds only to changes of the magnetic field.

This condition is used as follows. If the intruder is slightly familiarwith the disclosed intrusion alarm system, he may attempt to disable itby cutting the loop wires where they enter the first operationalamplifier 66. However, if this is done, it removes the quiescent smallvoltage at the input terminal of the operational amplifier, causing itsoutput 77 to drop to a negative voltage, thus causing conduction ofdiode 92 through resistor 89. This action, in turn, causes transistor 83to conduct, thus activating relay 88 through transistors 84 and 85. Inthis way, the receiver circuit protects itself against disablement.

Referring now to FIGS. 8 and 9 in which there is shown an alternativearrangement of an electromechanical pulsing unit, generally indicated at100, the unit is designed to send intermittent pulses of electricityfrom the vehicles battery through sending loop 26, as hereinbeforedescribed. Included in the unit 100 is a pulser circuit 102 comprising atransistor 103, and a resistor 105 which receives the potential from thevehicle battery 106. When switch 28 opens, transistor 103 conducts,startingmotor 107 and causing a 10 to 15 rotation of a cam 108 (alsoillustrated in FIG. 9). The cam is provided with a plurality of camheads 109 and oppositely-disposed magnets 110 and 111, respectively. Atleast one of said magnets is always positioned opposite to that of amotor-winding, starter switch 112. As the transistor 103 energizes themotor winding 107, the cam plate rotates and magnet 110 is displaced,causing starter switch 112 to close, whereby the motor continues torotate a one-half revolution, permitting magnet 111 to be oppositelypositioned to that of the starter switch 112. When the cam is rotating,the cam heads 109 contact a cam follower 113 of the switch 114, therebymaking and breaking contact when said cam is turning. This then suppliescurrent to the sending loop 26 which is pulsed at a rate depending uponthe revolution of the motor. Pulses are supplied during the one-halfrevolution of the cam, that is until one of the magnets 110 or 111 comeswithin range of the switch 1 12, at which time the motor turns off.

Summary It may thus be realized that the disclosed Intrusion AlarmSystem hasinnumerable advantages over priorart systems. First of all, itcannot produce nuisance false alarms during the vehicles normal dailyactivities. Secondly, when the vehicle is parked at a protected parkinglot, the system automatically goes into operation, so that there is nodanger of a person forgetting to turn on the system. Thirdly, anintruder need merely open any of the vehicles doors to produce an alarm.Fourthly, a late-arriving vehicle may even be parked adjacent to theprotected parking lot in order to be covered by the system. Fifthly, thetruck-mounted components can be easily transferred to another vehicle.Sixthly, the system offers self-protection against tampering. Seventhly,the system offers self-protection against tire theft by use of mercuryswitches to alarm whenever the vehicle is raised. Eighthly, a pluralityof different types of alarms may be used. And, finally, the overallsystem is simple, economical, easy to install, and readily manufactured.

We claim:

1. The combination comprising:

a pickup wire, said pickup wire being adapted to produce a signalvoltage when exposed to a changing magnetic field;

a vehicle having at least one door, said vehicle being parked adjacentsaid pickup wire; transmitter means, associated with said door, forproducing a changing magnetic field in the vicinity of said pickup wirewhen said door is opened, whereby said pickup wire transmits said signalvoltage;

receiver means, associated with said pickup wire, for producing an alarmon the occurrence of said signal voltage.

2. The combination of claim 1 wherein said receiver means comprisescontrol means for amplifying said signal voltage.

3. The combination of claim 2 including utilization means for producingan alarm when actuated by said amplified signal voltage from saidcontrol means.

4. The combination of claim 3 wherein said pickup wire comprises apickup loop positioned peripherally around a parking lot.

5. The combination of claim 4 wherein said utilization means comprises ahorn.

6. The combination of claim 4 wherein said utilization means comprises aflashing light.

7. The combination of claim 4 wherein said utilization means comprises arotating-lightbeam, air-patrol light.

8. The combination of claim 4 wherein said utilization means comprises aself-dialer.

9. The combination of claim 4 wherein said transmitter means comprises apermanent magnet affixed to said door, said permanent magnet having anassociated magnetic field that changes the ambient magnetic field atsaid pickup wire when said door is being opened.

10. The combination of claim 9 wherein said pickup loop comprises aplurality of secondary loops disposed within a given area in parkingspaces of said parking lot.

11. The combination of claim 4 wherein said transmitter means comprisesa sending loop positioned in said vehicle, pulsing means for causingsaid sending loop to conduct at least one pulse of electric current thatproduces a changing magnetic field, and switch means for activating saidpulsing means when said door is open.

12. The combination of claim 4 wherein said receiver means includes acircuit protection means, whereby said receiver means protects itselfagainst disablement of said loop.

13. The combination of claim 12 wherein said circuit protection meanscomprises a capacitor to perform as a low pass filter to reject 60H:power line interference, a second capacitor, a resistor in conjunctionwith said second capacitor forming a high pass filter, whereby thecombination of said low pass filter and said high pass filter form aneffective band pass characteristic.

14. The combination of claim 1 1 wherein said switch means comprises amagnetic-reed switch mounted on said vehicle in proximity to said door;and means, comprising a magnet mounted on said door, for holding saidmagnetic-reed switch in a quiescent condition.

15. The combination of claim 11 wherein said pulsing means comprisestiming means for disabling said ulsm meansaft ra r determined timeinterval.

16 T e combination 0? claim 11 wherein said pulsing means comprises anoscillator circuit, a flipflop circuit, means for applying the output ofsaid oscillator circuit to said flip-flop circuit for causing saidflipflop circuit to produce a train of reversing waveforms; and meansfor applying said reversing waveforms to said sending loop, whereby saidsending loop produces said changing magnetic field.

17. The combination of claim 11 wherein said pulsing means comprises apulsing circuit having a motor therein and a cam means for controllingsaid movement of said motor.

18. The combination of claim 11 wherein said switch means includes aplurality of mercury switches centrally positioned at each end of saidvehicle.

19. The combination of claim 14 wherein said receiving means includescounting means, and disabling means for causing said counting means todisable said control means for a given time interval, whereby thedisabled time interval prevents the production of false alarms.

1. The combination comprising: a pickup wire, said pickup wire beingadapted to produce a signal voltage when exposed to a changing magneticfield; a vehicle having at least one door, said vehicle being parkedadjacent said pickup wire; transmitter means, associated with said door,for producing a changing magnetic field in the vicinity of said pickupwire when said door is opened, whereby said pickup wire transmits saidsignal voltage; receiver means, associated with said pickup wire, forproducing an alarm on the occurrence of said signal voltage.
 2. Thecombination of claim 1 wherein said receiver means comprises controlmeans for amplifying said signal voltage.
 3. The combination of claim 2including utilization means for producing an alarm when actuated by saidamplified signal voltage from said control means.
 4. The combination ofclaim 3 wherein said pickup wire comprises a pickup loop positionedperipherally around a parking lot.
 5. The combination of claim 4 whereinsaid utilization means comprises a horn.
 6. The combination of claim 4wherein said utilization means comprises a flashing light.
 7. Thecombination of claim 4 wherein said utilization means comprises arotating-lightbeam, air-patrol light.
 8. The combination of clAim 4wherein said utilization means comprises a self-dialer.
 9. Thecombination of claim 4 wherein said transmitter means comprises apermanent magnet affixed to said door, said permanent magnet having anassociated magnetic field that changes the ambient magnetic field atsaid pickup wire when said door is being opened.
 10. The combination ofclaim 9 wherein said pickup loop comprises a plurality of secondaryloops disposed within a given area in parking spaces of said parkinglot.
 11. The combination of claim 4 wherein said transmitter meanscomprises a sending loop positioned in said vehicle, pulsing means forcausing said sending loop to conduct at least one pulse of electriccurrent that produces a changing magnetic field, and switch means foractivating said pulsing means when said door is open.
 12. Thecombination of claim 4 wherein said receiver means includes a circuitprotection means, whereby said receiver means protects itself againstdisablement of said loop.
 13. The combination of claim 12 wherein saidcircuit protection means comprises a capacitor to perform as a low passfilter to reject 60Hz power line interference, a second capacitor, aresistor in conjunction with said second capacitor forming a high passfilter, whereby the combination of said low pass filter and said highpass filter form an effective band pass characteristic.
 14. Thecombination of claim 11 wherein said switch means comprises amagnetic-reed switch mounted on said vehicle in proximity to said door;and means, comprising a magnet mounted on said door, for holding saidmagnetic-reed switch in a quiescent condition.
 15. The combination ofclaim 11 wherein said pulsing means comprises timing means for disablingsaid pulsing means after a predetermined time interval.
 16. Thecombination of claim 11 wherein said pulsing means comprises anoscillator circuit, a flip-flop circuit, means for applying the outputof said oscillator circuit to said flip-flop circuit for causing saidflip-flop circuit to produce a train of reversing waveforms; and meansfor applying said reversing waveforms to said sending loop, whereby saidsending loop produces said changing magnetic field.
 17. The combinationof claim 11 wherein said pulsing means comprises a pulsing circuithaving a motor therein and a cam means for controlling said movement ofsaid motor.
 18. The combination of claim 11 wherein said switch meansincludes a plurality of mercury switches centrally positioned at eachend of said vehicle.
 19. The combination of claim 14 wherein saidreceiving means includes counting means, and disabling means for causingsaid counting means to disable said control means for a given timeinterval, whereby the disabled time interval prevents the production offalse alarms.